Key points about Equine Herpes from the American Veterinary Medical Association:

 - Equine herpesvirus myeloencephalopathy (EHM) is caused by equine herpesvirus-1 (EHV-1). The virus most commonly causes respiratory infection, and not all infected horses will develop EHM;

- EHV-1 is a normally occurring virus found in the equine population; this outbreak is not being caused by a new virus or a new strain of a virus;

- Signs of EHM in horses may include nasal discharge, incoordination, weakness of the rear limbs and hind end, lethargy, urine dribbling, and decreased tail tone;
Llamas and alpacas can also be infected with EHV-1 and may develop neurologic disease;

- Currently, there is no equine vaccine that has a label claim for protection against EHM; There is no specific treatment that has been proven effective for EHM;
If your horse has potentially been exposed to an infected horse (or through contact with people or equipment that have been in contact with an infected horse), or is showing signs that could indicate EHM, quarantine your horse and other potentially exposed horses and contact your veterinarian.

Equine Herpes Prevention

by H.D. Atherton DVM, BS

Equine hepres virus (EHV) is known as "Snots",    rhinopneumonitis,                                and equine abortion virus.


 The most devistating affects of EHV-1 are abortions, foal illness & deaths; and meningitis like neuologic problems.

EHV types 1 & 4 cause snots and fever, but EHV-1 can cause abortions, foal deaths and paralysis at any age.

Transmission can be direct, nose to nose. It may be aerosolized by a sneeze and travel up to 35 feet. Contacting infected placentas and associated fluids can spread the disease. As well as fomites, such as tack, buckets, clothing, grooming equipment, bedding and boots.


The main contributors to rapid spread of infection are:


-Unrestricted movement of horses

-Reduced ventilation in barns


The most effective preventative measure is to minimize exposure of horses to sources of virus.

EHV can survive in the environment and on surfaces for at least a week and up to a month, but luckily it is easily killed by most disinfectants.

Remove manure, clean with soap and detergent, rise with water and disinfect.

**The current EHV vaccines have been shown to help minimize the severity of respiratory disease which decreases spreading of the disease.**


Horse infection control programs that are not dependent solely on vaccination are important.


Potential for loses during an outbreak of EHV-1 is directly related to herd size. For maximal protaction, group size should be as small as the physical facilities allow under conditions to limit the transmission of virus between established groups.

If feasible, horses should be segregated into groups that avoid the mixing of yearlings with older animals, pregnant with non-pregnant mares, horses with donkeys, etc. Consult with Dr. Harvey for further information on how to protect pregnant mares.

Prevent any inadvertant contact outside isolated groups.

Maintain a space barrier of 35 feet between paddocks to reduce transmission.

*Avoid exposure of intermingled groups of horses from diverse sources. Such as sales, shows, competitions and training centers.


Always remember herpes infections are for life, you can not get rid of it. Thus all horses, even normal horses, should be considered potential carriers of EHV. The addition of new animals should be preceded by a 1 month period of isolation.

A horse temprarily removed from a group, for a show or competition, should also have a 4 week isolation period prior to being reintroduced back into the group.

Any horse previously infected with EHV should be regarded as a potential and permanent source of infection for others horses and its surroundings. Herpes is a life long condition.

The latently infected horse is usually a silent carrier who, in response to external stressors, sheds infectious EHV into the environment. Examples include: Weaning, castration, relocation and terminal illness.

Due to the high prevelance of EHV latency in horses it is difficult to identify and seperate these carriers from the herd.

Measures to control the reactivation of latent EHV are aimed at controlling stress. Avoid crowding, poor nutritional state, heavy parasite infestation, lengthy transport, disruption of established social groups, harsh weather and other disease states.


Surveillance in an outbreak:

Monitor rectal temps of individuals. Horses that are infected with EHV usually spike a fever, even if there are no other signs.

Fevers can range from 102 - 107 F.

During the severe 2003 outbreak of neurologic EHV at the University of Findlay, Ohio, the prophylactic use and or early therapeutic use of Acyclovir appeared to be associated with survival.  



Vaccination alone is not enough

Isolation of smaller groups of similar types of horses is important

Quarantine ALL horses that arrive at a facility

Reduce stress and fomites

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